This is the one question I ask the most when students' grades are starting to go downhill: Are you getting enough sleep? Current research shows that middle school students should get 9 - 12 hours and teenagers should get 8 - 10 hours of sleep each night. This is very important for proper functioning of the brain. Sleep is also when the things we learn are locked into our memory.
Make sure you children are eating healthy meals and getting plenty of sleep. These are the best things you, as a parent, can do to ensure they are performing at their best.